Kelvin temperature from heat attribute
Yes. Multiply it by 1000.

Temperature
Gives a scalar defining the temperature of the volume. Values in the range 0..1 map to 0..1000 kelvin. This may be used to render physically-based fire with the Blackbody or Principled Volume shaders. All three outputs are the same.

From https://docs.blender.org/manual/en/dev/render/cycles/nodes/types/input/attribute.html
So the attribute node gives the temperature in Kelvins in the range [0,1000] mapped linearly to the range [0,1]. To change it back, you can simply multiply it by 1000.
Interestingly, what seems to refer explicitly to &quot;Temperature&quot; is actually referencing the &quot;heat&quot; attribute. using &quot;temperature&quot; in the attribute node simply returns 0, as if it were any undefined token.